George and Harold, in a twist they'd never have seen coming, must find adults they can trust to help them out of a stinky situation. Their gym teacher has acquired to turn children into obedient goody goodies, and our heroes must stop him before they too fall victim to his foul miasma. But with even their own parents favorably impressed by the good children, George and Harold must take drastic action--the only adults they can trust are their own future selves! So they travel to the future, to bring their adult-selves into the battle in the present.

It was fun to see their grown-up selves! George and Harold are unencumbered by deep reflections on the paradoxes of time travel, so there were no particularly worrying concerns about altering the future. This is about as worried as anyone gets, and made me chuckle:

"Wait a minute," said Old Harold. "I don't remember doing any of this when we were kids, do you, George?"

"No," said Old George. "If this happened in our past, how come we have no memory of it?"

"I don't know," said Harold.

"Probably bad writing," said George.

As an added time travel bonus, George and Harold get to read one of the graphic novels their adult selves have published (an us readers get a peak at it ourselves!).

But in a twist I never saw coming, Captain Underpants might have fought his last battle! Will this, the 12th book, be his last?????

It's as funny as all the other Captain Underpants books, and fans of the series will enjoy it.